Sucrose synthase (SuSy) is a key enzyme in the breakdown of sucrose in all plant sink tissue, including grain and fruit and has been extensively studied in many plants. Only relatively recently, however, have this protein and gene been characterized from cotton. The full length (2625 bp) of cotton sucrose synthase (SuSy) was isolated by Perez-Grau, L. and Delmer, D. in UC, Davis (accession number U73588) in May 1996. A 2030 bp of the same cDNA with 595 bp missing at the 5′ end was isolated by the same group in 1994 and was given to Prem Chourey in USDA/ARS for collaborative research. However, no evidence was available at that time regarding the role of this SuSy gene in cotton fiber/seed development, although it had been speculated (Amor et al., 1995) that part of the fiber localised SuSy could associate with cellulose synthase playing a role to channel carbon to this enzyme.
Evidence has been obtained that the expression of the SuSy gene could be important not only for cellulose synthesis but also for fiber cell initiation (thus may control fuzz) and a model on how sucrose is partitioned and competed for between fiber, seed coat and embryos of the cotton seed was proposed. These work were detailed in the following two papers: Ruan et al., 1997 Plant Physiology 115, 375-385; Ruan and Chourey, 1998, Plant Physiology 118, 399-406. More recently, the present inventors obtained further evidence supporting the hypothesis that SuSy plays a key role in mobilising sucrose into initiating fiber cells (Ruan et al., 2000 AJPP 27, 795-800).
The art is thus deficient in providing methods and means for altering the fiber development and properties in plants, particularly cotton, through alteration of sucrose synthase levels in cells of the plants.
These and other problems are solved as described hereinafter in the different embodiments and claims.
The present inventors have now obtained evidence regarding the role of SuSy in plant development and function through suppressing SuSy expression in transgenic cotton.